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CPR時增加胸部按壓時間可能增加心跳停止病患存活率
作者：Deborah Brauser  
出處：WebMD醫學新聞

　　September 18, 2009 — 根據線上發表在9月14日循環（Circulation）期刊的一項觀察性世代研究結果，在心肺復甦術（CPR）時，急救者增加花在胸部按壓的時間可以增加心跳停止病患存活率。
　　
　　溫哥華英屬哥倫比亞大學急診醫學臨床教授Jim Christenson醫師與其同事們寫到，院外心跳停止的存活率不一，但通常低於5%。
　　
　　雖然胸部按壓比例（CCF，花在進行胸部按壓時間比例）是CPR品質的重要部分，但在按壓時中斷是很常見的。研究者們報告，然而，動物實驗已經證實這些中斷降低冠狀動脈與腦部血流，使得存活預後較差。
　　
　　因此，研究者們想要藉由這項研究來評估CCF對院外心室顫動或無脈搏心室心搏過速病患，存活到出院的獨立效應。
　　
　　他們檢驗來自復甦預後社團心跳停止註冊試驗，一個包括在美國與加拿大、11個各自醫療醫學服務（EMS）的臨床中心團隊，為了進行院外心跳停止與外傷傷害治療的研究，總共從7個地點與78個單位收納了506位病患（平均年齡為64歲；80%為男性），所有病患皆在2005年12月到2007年3月之間在EMS到達後確認為心室顫動或心室心搏過速。
　　
　　除此之外，34%在公共場所心跳停止，71%被路人目擊、51%接受路人進行CPR。每位病患是否接受按壓、或按壓頻率都以自動體外去顫器測量。
　　
　　整體來說，117位病患（23%）出院時仍然存活。
　　
　　當CCF分別為0~20%時，回到自發性心跳的比例為58%，當CCF為21~40%時為73%，CCF為41~60%時為76%，CCF為61~80%時為73%，而CCF為81~100%時則是79%。
　　
　　當CCF為0~20%時，出院時仍然存活的比例為12%，CCF為21~40%時增加到22.9%，CCF為41~60%時為24.8%，CCF為61~80%時為28.7%；然而，當CCF為81~100%時，卻降到25%。
　　
　　作者們解釋，這些微的下降，他們稱為是個「令人好奇的發現」，可能是因為樣本數目太小與信賴限制較寬；另一個可能性是，CCF真正的高原效應高於80%。
　　
　　CCF每改變10%，對存活的估計校正線性勝算比為1.11（95%信賴區間為1.01-1.21）。
　　
　　這項研究的限制包括觀察性研究設計，只能觀察到CCF與存活之間的關係，而非因果關係，以及大部分的病例都來自於兩個現存具有分析心電圖描計的地點。
　　
　　試驗作者們表示，這些數據顯示CCF是改善突然心跳停止預後一個有效的方法；這項觀察是重要的，且提供復甦訓練與執業相對單純改變的原理，如果執行的話，將可能改善預後。
　　
　　作者們寫到，然而，仍然有許多問題沒有被回答，目前這項研究無法決定最佳的CCF，作為EMS訓練與品質改善的實際目標。
　　
　　Christenson醫師在新聞稿中表示，你對摯愛進行的胸部按壓是你可以做的最重要一部分，即使由他們執行，胸部按壓也確實有差異。
　　
　　預後研究社團由國家心臟、肺臟與血液機構一系列的合作協議，以及國家神經疾病與中風機構、美國陸軍醫學研究與物資司令部、加拿大健康機構循環與呼吸健康機構、加拿大國防研究與發展部、加拿大心臟與中風基金會、與美國心臟醫學會贊助這項研究。
　　
　　研究作者們表示已無相關資金上的往來。

Increasing Duration of Chest Compressions During CPR May Lead to Better Survival for Patients in Cardiac Arrest

By Deborah Brauser
Medscape Medical News

September 18, 2009 — Increasing the time that rescuers spend on chest compressions while performing cardiopulmonary resuscitation (CPR) could lead to increased survival in patients in cardiac arrest, according to results of an observational cohort study reported online September 14 in Circulation.

"Survival from out-of-hospital cardiac arrest is variable and often less than 5%," write Jim Christenson, MD, clinical professor of emergency medicine at the University of British Columbia in Vancouver, and colleagues.

Although chest compression fraction (CCF, the proportion of time spent performing chest compressions) is a vital part of quality CPR, interruptions during the compressions are common. However, animal studies have shown that these interruptions "decrease coronary and cerebral blood flow, which results in worse survival outcomes," report the study authors.

For this study, the investigators sought to estimate the independent effect of CCF on survival to hospital discharge in patients with out-of-hospital ventricular fibrillation or pulseless ventricular tachycardia.

They examined data from the Resuscitation Outcomes Consortium Cardiac Arrest Epistry, a group of 11 clinical centers with separate emergency medical service (EMS) agencies in the United States and Canada, formed to study out-of-hospital therapies for cardiac arrest and traumatic injury. A total of 506 patients (mean age, 64 years; 80% men) were enrolled from 7 sites and 78 agencies. All patients had confirmed ventricular fibrillation or ventricular tachycardia prior to EMS arrival between December 2005 and March 2007.

In addition, 34% arrested in a public location, 71% were witnessed by bystanders, and 51% received bystander CPR. The presence and frequency of chest compressions for each patient were measured with automated external defibrillators.

Overall, 117 of the patients (23%) survived to hospital discharge.

A return to spontaneous circulation was achieved 58% of the time when the CCF was 0% to 20%, 73% when the CCF was 21% to 40%, 76% when the CCF was 41% to 60%, 73% when the CCF was 61% to 80%, and 79% when the CCF was 81% to 100%.

Survival to hospital discharge occurred in 12% of the patients when the CCF was 0% to 20%, and increased to 22.9% when the CCF was 21% to 40%, 24.8% when the CCF was 41% to 60%, and 28.7% when the CCF was 61% to 80%. However, it dropped slightly, to 25%, when the CCF was 81% to 100%.

The authors explain that this slight drop, which they call "a curious finding," was likely due to the small sample size and wide confidence limits. Another possibility is "a true plateau effect of [CCF] above 80%."

The estimated adjusted linear effect on the odds ratio of survival for a 10% change in CCF was 1.11 (95% confidence interval, 1.01?- 1.21).

Limitations of the study include the observational study design, which allowed only an association between CCF and survival rather than a causal relation, and the fact that the majority of the cases were contributed by the 2 sites with a pre-existing ability to analyze electrocardiogram recordings.

"These data suggest that increasing [CCF] is an effective approach to improving outcomes from sudden cardiac arrest," write the study authors. "This observation is important and provides a rationale for relatively simple changes to resuscitation training and practice that are likely to improve survival if implemented."

They add, however, that many questions remain unanswered. "The optimal level of [CCF] that defines a practice goal for [EMS] training and quality improvement?.?.?. cannot be established by the present study," write the authors.

Dr. Christenson said in a press release, that "the chest compressions you do on a loved one are one of the most important things that can be done. Even by themselves, chest compressions can make a difference."

The Research Outcomes Consortium is supported by a series of cooperative agreements from the National Heart, Lung, and Blood Institute in partnership with the National Institute of Neurological Disorders and Stroke, US Army Medical Research & Material Command, the Canadian Institutes of Health Research-Institute of Circulatory and Respiratory Health, Defense Research and Development Canada, the Heart and Stroke Foundation of Canada, and the American Heart Association.

The study authors have disclosed no relevant financial relationships.

Circulation. Published online before print September 14, 2009.